The present invention relates to a mobile lifting crane that uses crawlers mounted on a carbody through a trunnion. The invention provides a way of easily installing the trunnion and connecting the crawler to the carbody when the crane is set up at a new job site.
Mobile lift cranes typically include a carbody having moveable ground engaging members; a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members; a boom pivotally mounted on a front portion of the rotating bed, with a load hoist line extending there from, and counterweight to help balance the crane when the crane lifts a load. There are different types of ground engaging members, most notably tires for truck mounted cranes, and crawlers. The crawlers typically have a frame, at least one drive tumbler supported on the frame; and a track made of a plurality of connected track shoes wrapped around the frame and engaging the drive tumbler so that a plurality of the shoes are in contact with the drive tumbler. Many cranes have two crawlers, one on each side of the carbody. However, there are some cranes that have four crawlers, two on each side of the carbody.
Because a mobile left crane is often used on uneven ground surfaces, there is a benefit for a crane having four crawlers to have each crawler mounted to the carbody in a manner that the crawler frame can pivot about a horizontal axis through which it is connected to the carbody. With such a pivoting movement, as the crane travels over uneven ground, the crawler can rotate with respect to the carbody as needed to best distribute the weight of the crane and any load being lifted. One method of mounting the crawlers to the carbody so that they can pivot is to use a trunnion. An example of a crane with four trunnion mounted crawlers is a Bucyrus Erie Model 300D dragline.
Since a crane will often be used in various locations, it needs to be designed so that it can be transported from one job site to the next. Moving a crane can be a formidable task when the machine is large and heavy. For example, highway limits on vehicle-axle loads must be observed and overhead obstacles can dictate long, inconvenient routings to the job site. One solution to improving the mobility of large construction machines, such as cranes, is to disassemble them into smaller, more easily handled components. The separate components can then be transported to the new job site where they are reassembled. For example, the typical practice has been to disconnect, remove, and transport the crawlers separately from the crane carbody. For a very large crane, it may also be necessary to separate the carbody into individual members. The ease with which the crane can be dismantled and set up has an impact on the total cost of using the crane. Thus, to the extent that fewer man-hours are needed to set up the crane, there is a direct advantage to the crane owner
In conventional cranes, each of the crawlers is typically bolted to the carbody of the crane. Because the connections between the crawlers and the crane carbody must sustain tremendous loads, the size and number of bolts used in these connections can be substantial. Accordingly, removing each of the crawlers from the carbody of the crane usually requires the loosening and removal of numerous large bolts from each of the crawler to carbody connections. Once the crane components are delivered to the new job site, then the crawlers must be carefully aligned with the carbody, and each of the bolts must then be re-inserted and tightened for each of the crawler-to-carbody connections. As a consequence, the disconnection and re-connection of the crawlers to the crane can be a difficult and time-consuming process.
One attempt to overcome some of the above-described problems is disclosed in U.S. Pat. No. 5,823,279 to Petzold, entitled “Carbody to Crawler Connection”, which issued Oct. 20, 1998. This patent discloses a carbody to crawler connection that utilizes a pair of pins. A vertical pin extends upwardly from the horizontal flange on the top of the carbody arm and is configured to loosely engage a hole in the horizontal flange on the top of the crawler frame weldment. A horizontal pin passes through lower portions of the vertical flanges of the carbody arm and the vertical flange of the crawler frame weldment. The crawler is attached to the carbody by first placing the hole in the horizontal flange on the top of the crawler frame weldment over the vertical pin on the top of the carbody arm. The hole in the vertical flange of the crawler frame weldment is then aligned with the holes in the vertical flanges of the carbody arm. The horizontal pin is then inserted through these holes to complete the connection.
The carbody to crawler connection disclosed in U.S. Pat. No. 5,823,279 has several advantages over the bolted-type connections typically used in conventional cranes. For example, this type of connection eliminates the need to carefully align and fasten numerous bolts. However, this type of connection does not allow the crawler to be attached by a trunnion so that the crawler may pivot about a horizontal axis. U.S. Pat. No. 7,007,764 discloses another carbody-to-crawler connection that has proved valuable for larger cranes, again allowing the crawlers to be easily and quickly removed and installed for crane transportation. However, again this type of connection does not allow for the use of a pivotal connection between the carbody and the crawler frame.
Thus there remains a need for a mechanism whereby a very large crane can be provided with crawlers that are mounted to a carbody with a pivotal connection that can be easily taken apart and reassembled, and preferably that can be used on a carbody that itself can be easily taken apart and transported and then reassembled at a new job site